1. Technical Field
This invention relates generally to electrical connectors and, more particularly, to a feedthrough connector for microwave integrated circuits.
2. Discussion
Microwave integrated circuits (MICs) often include a microstrip transmission line mounted on a conductive supporting substrate. The MIC is typically sealed within a hermetically sealed conductive package or housing and, therefore, the electrical connection from the MIC microstrip transmission line to another circuit component, such as a coaxial transmission line or another microstrip, must be made through a package wall.
Conventional rf feedthrough connectors used in this type of application typically have a cylindrically shaped outer conductor surrounding a co-axial inner conductive pin which is spaced from the outer conductor by a dielectric glass insulator. The outer conductor is sealed in an opening formed in a wall of the package housing and the center pin extends longitudinally into a package cavity. The MIC substrate is placed in the cavity and slid under the center pin. In order to electrically connect the pin to a microstrip transmission line on the substrate, a ribbon loop is made from the MIC microstrip line over the conductive pin.
However, connectors of this-type often possess several disadvantages which suggest the need for an alternative design. First, this type of conventional connector is not amenable to automated assembly procedures since the microstrip substrate must be slid underneath the protruding inner conductor. Accordingly, there is a danger of bending the extending inner conductor or creating a crack at the glass interface while sliding the substrate beneath the conductive pin, or while wirebonding the inner conductor to the MIC. The ribbon loop also tends to have a high inductance which undesirably increases the voltage standing wave ratio (VSWR).
Fabrication of a conventional feedthrough housing also tends to be expensive because it requires that individual components be held to tight tolerances in order to maintain a close clearance between the upper substrate surface and the underside of the inner conductor. Concentric holes of different diameters often need to be formed in the housing wall, one hole for the outer conductor and another through which the conductive pin protrudes. Solder typically used to seal the outer conductor in the housing wall opening can also flow into the hole through which the inner conductor extends into the package cavity, thereby creating the possibility of an electrical short.
U.S. Pat. No. 4,724,409 to Lehman, issued Feb. 9, 1988, attempts to provide an improvement over this type of conventional connector. This patent shows a connector having a cylindrical portion secured in an opening formed in a package wall and an adjoining semi-cylindrical portion which protrudes into the cavity in which the MIC or other circuit component is disposed. Upper portions of the outer conductor, dielectric insulating layer and inner conductor of the semi-cylindrical portion of the connector have been removed to form a planar upper surface on the portion of the connector which extends into the package cavity. The MIC is positioned within the cavity such that it abuts this semi-cylindrical portion and the exposed surface of the inner conductor is attached to a microstrip line on the MIC by a short ribbon or wire bond. Semi-cylindrical sections of the shield and dielectric layer support the inner conductor along its entire length from beneath.
However, the removal of upper portions of part of the connector to form a semi-cylindrical portion can cause the characteristic impedance of that portion of the connector to differ from that of the adjoining cylindrical portion. The resulting performance of the connector may be degraded by a nonuniform impedance along its length which can increase VSWR. This type of connector also has the disadvantage of requiring that the portion of the connector protruding into the cavity be machined to a length which ensures that it precisely abuts the MIC substrate, thereby increasing manufacturing difficulty and cost.
As such, it may be appreciated that there continues to be a need for a microwave feedthrough connector which provides reduced manufacturing cost and improved reliability through simplified connector construction, compatibility with automated assembly procedures and reduced VSWR.